The present invention relates to a system for automatically detecting the presence of moisture on a surface, such as the surface of a windshield of a vehicle for an automobile, in order to automatically actuate the vehicle""s windshield wipers and/or defroster or defogging system.
In conventional windshield wiper systems, the windshield wipers are actuated based on the elapsed time between wipes rather than the moisture level on the exterior of the windshield. During conditions of relatively consistent rainfall, for example, the time interval can be adjusted to correspond to the amount of time in which the rain accumulates to the point of the desired visibility level. Unfortunately, the rate of rainfall may vary dramatically over a given period of time. Additionally, traffic conditions may also cause varying amounts of rain to fall on the windshields, such as when a truck passes by. As a result, during such conditions, the driver must frequently adjust the wiper time interval, which can be cumbersome.
Various systems are known which automatically control the interval between wipes of the windshield wipers based upon moisture on the vehicle windshield. In some known systems, various coatings are applied to the vehicle windshield. Electrical measurement of those coatings is used to provide an indication of the moisture content on the windshield. Unfortunately, such methods require relatively expensive processes, which makes such systems commercially non-viable. Other systems for automatically sensing the moisture content on a vehicle windshield are also known. For example, optical systems are known which measure the difference of reflected light of a dry windshield versus a wet windshield. Unfortunately, such optical systems are susceptible to interference from external light sources and thus provide inadequate performance. Other known systems must be adhered to the windshield, which complicates the windshield replacement. As a result of such complications, moisture sensors are rarely found on vehicles.
Another system for automatically detecting the moisture content on a windshield is disclosed in Japanese Laid Open Patent Application No. Hei(1995)-286130, which describes the use of a charge coupled device (CCD) image sensor to image a portion of the vehicle windshield in order to detect raindrops. The system described therein computes the sum of the differences between each pixel and the average of all pixels. Unfortunately, headlamps of oncoming vehicles will create a bright spot in the image, which would be difficult to completely blur and likely be interpreted as rain. Moreover, in order for such a system to work effectively, distant objects within the imaged scene must be completely blurred. Otherwise, there will be dark and light regions in the imaged scene corresponding to the distant objects. Although there is no optical system disclosed in the Japanese laid open patent application for accomplishing this objective, it would be very difficult to develop an optical system to completely blur an oncoming headlamp. Failure to blur oncoming headlamps could cause false triggering of the system disclosed in the above-identified Japanese laid open patent application.
Another problem with automatic rain detection systems is the inability of the system to detect the operation of the windshield wipers. In certain cold climate conditions, the windshield wipers are known to freeze to the windshield. In such a situation, since the moisture is not being removed by the wipers, an automatic rain sensing device would continuously command the wipers to actuate, even though the wipers are frozen to the windshield, potentially damaging the windshield wiper system.
Another problem with known systems is the inability to detect fog on the interior and exterior of the windshields. As mentioned above, automatic moisture detection systems, such as disclosed in the above-identified Japanese laid open patent application, are based upon the ability to detect raindrops on the windshield. When a uniform fog or mist covers the vehicle windshield, systems, such as the system disclosed in the Japanese laid open patent application, are unable to sense such moisture on the exterior of the windshield. As a result, during such a condition, the windshield wipers will have to be manually actuated, thereby partially defeating the purpose of an automatic rain sensor and windshield wiper control system making the feature a lot less desirable.
In other situations, fog develops on the inside of the windshield independent of the moisture content on the exterior of the windshield. In such a condition, automatic rain sensing systems, such as disclosed in the Japanese laid open patent application, are unable to detect the moisture content on the exterior of the vehicle windshield until after the fog on the interior of the windshield is cleared. In such a condition, a defroster or defogger system would have to be manually actuated to remove the interior fog on the windshield. The automatic rain sensor would not be operable during such a condition until the fog on the interior of the windshield is sufficiently cleared.
In commonly assigned U.S. Pat. Nos. 5,923,027, 6,097,024, and 6,262,410, a moisture sensing system is disclosed that overcomes the problems noted above. Nevertheless, it would be desirable to further improve the ability of the disclosed system to distinguish from light sources within the imaged scene that may cause false triggering of the windshield wipers.
According to one embodiment of the present invention, a moisture sensing system is provided that comprises: a sensor that is divided into a plurality of subwindows each having a sensitivity that is variable independent of the other subwindows; an optical system operative to direct light rays from at least a portion of the surface onto the sensor; and a processing system in communication with the sensor and operative to adjust the sensitivity of the subwindows and to analyze data from the sensor to detect moisture on the surface.
According to another embodiment of the invention, a system is provided for detecting moisture on a surface that comprises: a sensor that is divided into a plurality of subwindows, at least one of the subwindows having a sensitivity that is independently variable; an optical system operative to direct light rays from at least a portion of the surface onto the sensor; and a processing system in communication with the sensor and operative independently to adjust the sensitivity of the at least one subwindow and to analyze data from the sensor to detect moisture on the surface.
According to another embodiment of the present invention, a windshield wiper control system for a vehicle is provided that comprises: a sensor that is divided into a plurality of subwindows; an optical system operative to direct light rays from at least a portion of the surface of the windshield onto the sensor; and a processing system in communication with the sensor and operative to analyze data from the sensor to determine whether moisture is detected in each subwindow and to control the windshield wipers based upon a number of subwindows in which moisture is detected.
According to another embodiment of the present invention, a windshield wiper control system for a vehicle is provided that comprises: a sensor; an optical system operative to direct light rays from at least a portion of the surface of the windshield onto the sensor; and a processing system in communication with the sensor and operative to analyze data from the sensor to detect moisture on the windshield and to automatically activate the windshield wipers when moisture is detected. The processing system is responsive to at least one remote device to enable or disable automatic control of the windshield wipers.
According to another embodiment of the present invention, a system for detecting moisture on a surface is provided that comprises: an image sensor array including a plurality of light sensors; an optical system operative to image at least a portion of the surface onto the image sensor array; a supplemental illuminator for selectively illuminating the portion of the surface imaged onto the image sensor array; memory for storing a first image obtained by the image sensor array when the supplemental illuminator is illuminating the portion of the surface, and for storing a second image obtained by the image sensor array when the supplemental illuminator is not illuminating the portion of the surface; and a processing system in communication with the memory, the supplemental illuminator, and the image sensor array. The processing system is operative to compare the first and second images stored in the memory and to analyze results of the comparison to detect moisture on the surface.
According to another embodiment of the present invention, a fog detector system is provided for detecting fog on an inside surface of a vehicle window. The fog detector system comprises: an emitter for selectively projecting radiation onto a region of the inside surface of the vehicle window; a sensor disposed with its optical axis substantially in parallel with that of the emitter, the sensor being sensitive to the radiation projected by the emitter for sensing levels of incident radiation both when the emitter projects radiation and when the emitter does not project radiation; and a control circuit coupled to the emitter for selectively activating the emitter, and coupled to the sensor for receiving signals from the sensor representing the level of incident radiation. The control circuit determines the difference between levels of incident radiation when the emitter is activated and when the emitter is deactivated, and compares the difference to a threshold to determine whether fog is present. When fog is present, the control circuit generates a signal indicating the presence of fog on the vehicle window.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.